Strip thickness control apparatus for a rolling mill



Aug. 8, 1967 A. HEINDEL ETAL.

STRIP THICKNESS CONTROL APPARATUS FOR A ROLLING MILL Filed Nov. 29, 1963 mQJDomm ommaw W nv N m WITNESSES gmx/6V United States Patent O 3,334,502 STRIP THICKNESS CONTROL APPARATUS FOR A ROLLING MILL Adolf Heindel and Ingemar Neuler, Erlangen, Germany,

assignors to Siemens-Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Filed Nov. 29, 1963, Ser. No. 327,027 Claims priority, application Germany, Dec. 24, 1962, S 83,052 7 Claims. (Cl. 729) The present invention relates in general to strip thickness control apparatus and more particularly to strip thickness control apparatus for a rolling mill having a plurality of stands and wherein at least one between stand sag or tension regulator is provided.

For various reasons, such as lack of space, large thickness of rolling billet, scale on the workpiece and the like, the attainment of the requisite thickness of delivery rolled strip during hot rolling entails certain difculties, especially at the rst set of rolls. Since the thickness of the strip emerging from a rolling mill is, to a large approximation, equal to the gap between the rolls of the last stand, it would seem obvious to keep this last stand roll spacing or gap constant. However, it is only possible to measure this roll gap by indirect methods which depend on the rolling pressure and which can be determined either by special pressure pickups such as piezo-electric gauges or by measuring the expansion of the stand framework. These well-known procedures are complicated and of low accuracy because it is not possible, either in whole or in part, to account for the many extraneous disturbing influences.

The present invention proposes an alternative and simpler method of controlling the delivery thickness of strip during the hot rolling process. It originates from the realization that if we are to have an unchanged exit velocity from a given stand, any change in strip thickness or change in roll gap of that stand must inevitably result in a change in the entrance velocity of the rolled stock. This is because, according to the well-known principle of continuity, the amount of stock being fed into the rolls of a given mill stand in a specied time interval must be equal to the amount of rolled stock emerging therefrom, the width of the strip being considered as remaining constant.

The lpresent invention is concerned with an apparatus for regulating the thickness of the rolled stock in hotmill trains having a plurality of mill stands and having sag (curl, bow) or tension controllers located between the individual stands or sets of rolls. The drive-motors of the plurality of stands are regulated `with respect to each other so as to have a chosen ratio of revolutions per minute. A regulator is associated with each individual sag-lifter or interstand tension controller and controls the angular tilt or position of the said sag lifter arm to a preset value with respect to the setting of the succeeding stand roll spacing. In this connection, it is advantageous to employ a regulator which operates proportionately, to control the succeeding stand screwdown servo-motor Since this regulation is associated with a specific time constant, it would be advantageous to anticipate the possibility of controlling the variations in the sag or interstand tension between the roll stands via the number of revolutions per minute of a preceding stand. But since only an integral-operating regulator has been employed for the purpose of controlling the extent of the sag via the rpm., a proportional regulator will now be employed in accordance with the invention superimposed on the conventional rpm. or speed controller of the associated succeeding stand roll motor, and providing it with an additional pre-set (or required) value as a function of the change in angle of the sag-regulator. The rpm. or speed regulator can, for example, have proportional-integral characteristics if desired. It is an object of this invention to provide an improved strip thickness control apparatus for a rolling mill operative to better control the delilvery thickness of strip delivered from that rolling mil The invention will now be described. in greater detail on the basis ofthe attached drawing.

The drawing shows a multiple stand hot-rolling mill train, in which only the rst stand 10, the second stand 12 and the last stand 14 are shown in the figure. The rolling-stock or workpiece strip is denoted by the numeral 2. The rolling direction runs from left to right, as shown by the arrow. Each set or stand of rolls is driven by la roll motor M to which is connected a revolution speed (rpm.) controller 3, and fed into one side of the latter for each stand in conventional manner is the true r.p.m. from a tachometer T1 and the required (pre-set) value given as a speed reference by potentiometer 4. These required value or speed reference potentiometers may be connected to a common voltage lead and be so adjusted that the individual stand roll-motors have the required rpm. or speed ratio with respect to each other as presently well known in this vart and corresponding to the reduction in thickness of roll-stock 2 in the individual roll stands. The gap between the rolls of the individual mill stands is adjustable via a screwdown servo-motor 5 controlled by ia conventional rpm. regulator 8 for ne adjustment in accord with the existing rolling program, the regulator 8 being fed with the required value as a position reference signal through input connection 18 and with the actual value by the tachometer T2. Between the individual rolling mill stands is located a sag-lifter or tension controller 6 to which is connected a measured-value transducer or thickness gauge transducer 7 which yields a measurement signal as a proportional function of the sag-lifter angle a. The actual means for raising and positioning the sag-litters is well known per se `and is not specifically shown.

As mentioned above, it is desired to provide a substantially constant rate of revolution or constant exit velocity relationship between the two neighboring sets of rolls with the permissible assumption 4in the case of strip rolling of a constant strip Width, so as to maintain the relationship that v1d1=v2d2, where v1 and v2 are the velocities and d, and d2 are the thickness of the in-going and emerging strip passing through the rolls of a given stand. When, as a consequence of a change in the rollstock temperature, for example, the emerging strip thickness or d2 undergoes `a change, but the exit velocity v2 remains constant, it follows that the input velocity v1 must change with the result that the amount of sag in front of the particular roll will increase. As a result, there is a change in the sag-lifter angle a that is a measure of the change occurring in the emerging strip thickness d2. It follows that the regulation deviation or error signal Aa is formed in an accommodating transducing and comparison apparatus 7, operative with the actual sag lifter angle a applied to one of its inputs and the reference or desired angle supplied to the other input. This error signal Aa is amplied in a proportional amplifier 11 and serves as the desired value at the rpm. regulator 8 for the servo-motor 5. Accompanying ya variation in the angle a of the sag-lifter from the required value pre-set by 9, the roll gap of the succeeding stand is altered via servo-motor 5 with a velocity proportional to the regulator variation Aa until sag-lifter `6 again yreaches the required position. When this occurs, the succeeding stand roll gap, and hence the roll-stock emerging strip thickness d2, will have again attained the requisite dimensions.

Simultaneously with the above, the deviation Aa provided by transducer is fed into `a proportional amplifier 20. Transducer 7 and amplifier 20 thus form a proportional -regulator which is operative with the r.p.m. controller 3 of the succeeding roll unit and provides it with an additional control signal. By this means the succeeding stand r.p.m. controller 3 ensures a speedy restoration of the sag in the strip head of that stand to its pre-established or desired value should any undesired change occur therein. Since amplifier 20 in association with transducer 7 effectively from a proportional regulator, a departure from the desired or reference angle a will at times be present and, corresponding to this departure Aa from the required value of sag, the succeeding stand screwdown setting will be adjusted with regard to the integrallyoperating regulators 5 and 8 until the sag attains the precise degree of angle a of sag required. When this occurs the succeeding stand the roll-gap, and hence the emerging strip thickness d2 of roll-stock, will have again attained the pre-arranged or desired value.

At the same time, the control-deviation signal Aa supplied -by transducer 7 is fed into the proportional amplifier 20. Transducer 7 and amplifier 20 for each stand thus form a proportional regulator which is operative with the rotational speed regulator 3 of the succeeding roll unit and provides it with an additional required or control signal value. As a result, this speed regulator 3 promotes the rapid return of the sag Iahead of that stand to the required value should any change in the strip sag occur. Since amplifier 10 in association with transducer 7 effectively form a proportional regulator, there will at times be present a Certain control difference-signal, and corresponding to this deviation from the required value, the succeeding stand screwdown position will be so adjusted through the integral-operating regulators 5 and 8 until the strip sag accurately attains the desired value. As a consequence, the resulting transitory change in the succeeding stand r.p.m. is 'cancelled via amplifier 20 and r.p.m. regulator 3 so that the feed velocity v1 and the exit velocity v2 return to their original values. This means the thickness d2 of the emerging roll-stock is likewise restored to its desired and preset value.

Instead of employing two separate amplifiers 20 and 11 for the departure Aa from the regulated value of a, a single and common error signal amplifier can, of course, be employed for this purpose.

During the above described procedure for regulating the roll-stock thickness by controlling the amount of sag with regard to each individual stand, the introduction of correction terms, such as, for example, -those for the ternperature caused expansion of the rolls and mill stand frame, for changes in the play of the bearings, heating during rolling and the like become superfluous and unnecessary per se, the correction terms being inexact, and, until now, accompanied with difliculties when used to control the thickness in conventional rand previous control apparatus for rolling-mills. The subdivision of the variations in sag in a portion or section of roll stock which affects the r.p.m. in altransitory fashion, and the subdivision in a section of roll stock which on remaining regulates or re-sets the succeeding stand screwdown position, together guarantee the controlling of the roll-stock feed land exit velocities, as 'well as providing a better control for transitory perturbations occurring, for example, in the cont-rol devices including the rectifier which is controlled by the regulators and which feeds the motors.

With the arrangement described, a high constancy is attained in the thickness d2 of the strip emerging from the last set of rolls or stand 14, provided that the thickness of strip fed into the first set of rolls remains substantially constant. Thus, it could be advantageous to control the thickness of the strip leaving the first set of rolls 10 as constant as possible. As may be envisaged, any changes in the thickness of strip being fed into the the second set of rolls 12 will also produce proportional changes in the thickness of the strip emerging from the last set of rolls 14. However, on account of the large reduction in thickness in the strip rolling mills, these variations are relatively small. In order to control the variations until they reach negligible proportions, the thickness of the strip from the last stand 14 can be measured by means of a thickness gauge V22. located behind the last set of rolls 14, the thickness gauge 22 consisting, for example, of a radiography or X-ray apparatus, and, by means of a regulator 13, which can be supplied by a reference signal device 24 with the required thickness value, each that an additional correction signal can be applied to r.p.m. regulator 3 of the last of rolls 14. This correction produces a change in the r.p.m. of the roll motor for the last stand or set of rolls 14 in such a sense that a correction is applied to the roll-gap in conjunction with the change in the angle of the sag-lifter operative with the regulators 5 and 8. lf, for example, the exit thickness d2 from stand 14 is too large as measured by thickness gauge 22, it then follows that the thickness correction signal impressed by regulator 13 on the r.p.m. controller 3 for the last stand 14 produces a corresponding increase in the r.p.m. of the drive motor, and hence a reduction in the angle a of the sag-lifter placed ahead of the last stand 14. This causes the screw-down regulator 8 for the last stand 14 to cause a corresponding reduction of the roll-gap in order to re-establish the original saglifter angle and by this means corrects the strip exit thickness d2 from the last stand 14 to the desired value. The effect of sag regulator 20 on r.p.m. controller 3 can be weakened or augmented as may be desired for any particular strip rolling operation by the provision of the thickness correction signal supplied by thickness regulator 13.

We claim as our invention:

1. In thickness control apparatus for a strip rolling mill having a pair of spaced roll members, the combination of strip deflection sensing means responsive to the actual deflection of said strip prior to passing between said roll members, driving means for said roll members to provide a desired operating speed to said roll members, spacing control means for said roll members to provide a desired spacing between said roll members, and thickness control means operative with each of said driving means, said spacing control means and said strip deflection sensing means to control the thickness of said strip emerging from said roll members in accordance with a predetermined deflection error relationship between said actual strip deflection and a desired strip deflection for said strip prior to said roll members.

2. In control apparatus for the thickness of a strip operative with a pair of spaced roll members in a strip rolling mill, the combination of strip tension sensing means for providing a control signal in response to the actual tension of said strip prior to passing between said roll members, driving means for said roll members to provide a desired operating speed to said roll members, spacing control means for said roll members to provide a desired spacing between said roll members, and thickness control means operative with at least one of said driving means and said spacing control means and responsive to said control signal to control the thickness of said strip emerging from said roll members in accordance with a predetermined deflection error relationship between said actual strip deflection and a desired strip deflection prior to said roll members.

3. In thickness control apparatus for a strip rolling rnill having a pair of spaced roll members, the combina-, tion of strip deflection sensing means for providing a control signal in accordance with the deflection error difference between the actual deflection of said strip at a predetermined location prior to passing between said rollV members as compared to a desired deflectionof said strip, driving means for said rolls members to provide a desired operating speed to said roll members, screwdown control means for said roll members to provide a desired spacing between said roll members, and thickness control means operative with said driving means and said spacing control means in response to said control signal to control the thickness of said strip emerging from said roll members.

4. In thickness control apparatus for a strip rolling mill having a plurality of roll stands each including a pair of spaced roll members, the combination of strip deflection means positioned ahead of each pair of spaced roll members and respectively providing a control signal in accord ance with a pretermined deflection error of the strip ahead of each pair of spaced roll members, driving means for each pair of roll members to provide a desired operating speed relationship between said plurality of roll stands, spacing control means for each pair of spaced roll members for providing a desired spacing between said pair of roll members, and deflection control means operative with said strip deflection means for each respective pair of spaced roll members and said spacing control for each respective pair of spaced roll members for controlling the deflection of said strip ahead of said pair of spaced roll members in response to said control signal in accordance with the deflection error of the strip ahead of said pair of spaced roll members.

5. In control apparatus for a strip rolling mill having a plurality of roll stands, with each roll stand including a pair of spaced roll members, the combination of a plurality of strip deection members, with each said deilection member being positioned ahead of a different pair of spaced roll members and providing a control signal in accordance with a predetermined deflection error of the strip ahead of its associated pair of spaced roll members, driving means for each pair of roll members to provide a desired operating speed relationship between said plurality of roll stands, thickness control means for each pair of spaced roll members for providing a desired spacing between said pair of roll members, and deflection control means operative with each pair of spaced roll members and with one of said strip deflection means and said spacing control means operative with its respective pair of spaced roll members for controlling the deiiection of said strip ahead of its respective pair of spaced roll members in response to said control signal from the strip deflection member positioned ahead of its respective pair of spaced roll members.

6. In thickness control apparatus for a strip rolling mill having a plurality of roll stands each including a pair of spaced roll members, the combination of strip deection means positioned ahead of at least one pair of spaced roll members and respectively providing a control signal in accordance with a predetermined deflection error of the strip ahead of said one pair of spaced roll members, driving means for each pair of roll members to provide a desired operating speed relationship between said plurality of roll stands, strip thickness control means for at least said one pair of spaced roll members for providing a desired spacing between said pair of roll members, and deilection control means operative with one of said strip deflection means and said spacing, control means for said one pair of spaced r-oll members for controlling the deflection of said strip ahead of said one pair of spaced roll members in response to said control signal, with said deflection control means including a signal integrating device having an integral characteristic in accordance with the deflection error of said strip ahead of said one pair of spaced roll members.

7. In thickness control apparatus for a strip rolling mill having a plurality of roll stands each including a pair of spaced roll members, the combination of strip deilection means positioned ahead of one pair of spaced roll members and respectively providing a control signal in accordance with a predetermined deflection error of the strip ahead of each said one pair of spaced roll members, driving means for each pair of roll members to provide a desired operating speed relationship between said plurality of roll stands, strip thickness control means for said one pair of spaced roll members for providing a desired spacing between said one pair of roll members, deection control means operative with said spacing control means for said one pair of spaced roll members for controlling the deflection of said strip ahead of said one pair of spaced roll members in response to said control signal, and strip thickness measuring means operative with the strip leaving said one pair of spaced roll members for providing a thickness error correction signal to said spacing control means for additionally controlling the deflection of said strip ahead of said one pair of spaced roll members.

References Cited UNITED STATES PATENTS 2,189,609 2/ 1940 Lessmann 72-12 2,297,812 10'/ 1942 Stoltz 72--9 2,715,702 8/ 1955 Winchester 729 2,851,911 9/1958 Hessenberg 7212 3,186,200 6/1965 Maxwell 18-2 X 3,253,438v 5/1966 Stringer 72-12 RICHARD J. HERBST, Primary Examiner. 

1. IN THICKNESS CONTROL APPARATUS FOR A STRIP ROLLING MILL HAVING A PAIR OF SPACED ROLL MEMBERS, THE COMBINATION OF STRIP DEFLECTION SENSING MEANS RESPONSIVE TO THE ACTUAL DEFLECTION OF SAID STRIP PRIOR TO PASSING BETWEEN SAID ROLL MEMBERS, DRIVING MEANS FOR SAID ROLL LMEMBERS TO PROVIDE A DESIRED OPERATING SPEED TO SAID ROLL MEMBERS, SPACING CONTROL MEANS FOR SAID ROLL MEMBERS TO PROVIDE A DESIRED SPACING BETWEEN SAID ROLL MEMBERS, AND THICKNESS CONTROL MEANS OPERATIVE WITH EACH OF SAID DRIVING MEANS, SAID SPACING CONTROL MEANS AND SAID STRIP DEFLECTION SENSING MEANS TO CONTROL THE THICKNESS OF SAID STRIP EMERGING FROM SAID ROLL MEMBERS IN ACCORDANCE WITH A PREDETERMINED DEFLECTION ERROR RELATIONSHIP BETWEEN SAID ACTUAL STRIP DEFLECTION AND A DESIRED STRIP DEFLECTION FOR SAID STRIP PRIOR TO SAID ROLL MEMBERS. 